The invention relates to a particular method of purifying the exhaust gases of internal combustion engines, and to the benefits to engine construction, fuel conservation and power output that may arise out of the employment of these methods.
Because of the complexity of both the art and the scope of the method of exhaust emission control described, it is proposed to present this disclosure in several distinct sections comprising filamentary material, cold start and related features, reaction process, form of reactor housing, and materials and manufacturing methods generally.
Since all the materials used for any portion of the assembly must have certain features in common, such as heat and shock tolerance, abrasion and corrosion resistance, they have been described under a separate heading and not in relation to individual features, with the exception of certain isolated cases. The brief description of the drawings is continuous, but the discussion has been separated to the relevant sections. The reasons for these arrangements are both to make the location and cross-referencing of information easier and to help the reader to a clearer understanding of the invention.
It is well known that the art of cleaning exhaust gases (as opposed to the art of minimising the formation of pollutants at the point of combustion) is centred around the technique of speeding up chemical reactions normally tending to continue in the exhaust gases at a slow rate, and that this speeding of chemical reaction is achieved by some combination of two basic means, namely the provision of catalytic agents and the encouragement of reaction under conditions of heat and/or pressure. The provision of extra air is often used to balance properly the chemical reaction to a desired configuration. These methods all involve a majority of common features, such as the employment of reaction chambers, the use of high temperature materials, such as ceramic, the provision of extra air, etc.
The object of the invention is to provide a means of removing noxious or undesirable elements from the exhaust gases from internal combustion, or other, engines, especially in the case of engines fitted in vehicles. The informed reader will no doubt be sufficiently aware of the general background to the desirability of cleaning exhaust gases and the history and progress of enforcing legislation, so obviating the need to explain these matters in detail here. Any knowledge of the matter must include an appreciation of the difficulties that have been encountered over the years, alluded to above, but were generally caused by the very sudden and great upsurge of activity in the field of emissions treatment, due to the promulgation of legislation initiated by the State of California and later the U.S. Federal Government. The suddenness (and often reluctance) with which the motor industry entered this field resulted in much systemless and unco-ordinated work, in which existing techniques and hardware were adapted to meet requirements rather than design approaches being conceived afresh. It is therefore a further object of the invention to overcome the many difficulties and penalties so far encountered with the current means of treating exhaust gases, which are described in greater detail below. The first generation of exhaust emission devices are being fitted to vehicles, for despite their disadvantages the emission laws must be met. It is felt that the present invention constitutes a very much improved second generation approach to the treatment of exhaust gases, for reasons explained in the disclosure.
In general, the problems of early emission systems may be classified under the following five headings, of which the last is perhaps the most important: Adaptability to be mounted on existing engines, ability to meet emission requirements whilst remaining durable, flexibility of design, cost of installation and maintenance, and cost of operating the engine and therefore the vehicle in which it might be installed. Considering first the question of adaptability to be mounted on existing engines, the known systems which offer the promise of good performance are all either very elaborate, involving the use of usually two separate reactors, air pump, exhaust gas recirculation (EGR) sensors, by-pass systems, etc., or they involve different engine configurations or design, as for example rotary, diesel and stratified charge engines. Under the latter circumstances, it is considered unreasonably expensive in terms of cost and effort to change the entire engine system, whilst the question of adapting an existing engine by fitment of existing technology involves such an increased volume of components that the adaption can rarely be made without extensive body and layout modifications. The cost of installing the complex equipment outside assembly-line situations would be very great. As will be seen, the present invention effectively eliminates the need for ancilliary equipment (if some is needed for the highest emission standards, a small sacrifice of performance would presumably prove acceptable for existing vehicles). In addition it is a simple device occuping no additional under-bonnet space, being substitutable for the existing exhaust manifold in a quick and inexpensive operation.
Making all vehicles sold or manufactured in a country conform to a common emissions requirement has generally been a slow and costly procedure. The present invention by its simplicity reduces the variables in practice to the one basic question of type and nature of core configuration. The housing involves no major problems or need for experimentation, and in use it is intended that common housings be adapted to differing engines of similar size or capacity, with core composition modified for the respective engines. Alternatively, a vehicle with the invention fitted could when exported be adapted for the requirements for different countries by substitution of core, without any modification to underbonnet or body layout.
The applicant feels that in the long term all emission treatment means will be thermally operative, rather than almost wholly catalytic as the majority of systems today, and this for reasons connected with hardware costs. Basically both heat or catalysts have been employed to achieve the same effect, that is to hasten reaction process. Catalysts are expensive to produce, need costly replacement or maintenance, while heat is available at no cost, since it has already been produced by the process of internal combustion. Therefore economic pressures will ensure that eventually gas treatment largely employs this readily available heat, and the consequent reduced cost of clean air will make its enforcement practical in areas of the world where it is today considered an uneconomic luxury. To properly use this heat, and thereby reduce ultimate cost, has been one of the prime objects of this invention. In addition to providing a system wherein catalysts have reduced power (and therefore cost), the invention allows for further economy of installation and maintenance in a number of ways. The present invention comprises a single reactor, operative in the tri-component mode, with further cost savings. Some embodiments involve the use of a single integral housing of high alumina ceramic, which can be manufactured relatively cheaply.
It is hoped that this background note, together with the detailed description which follows will enable the reader to understand fully the objects and advantages of the invention.